Answer:
y = -2x-13
1) plot the coordinate you have on a graph (starting at (0,0) move to the left until you hit -8 and then up until you are at +3)
2) Since your slope is negative the line will be higher on the left and lower on the right, so starting at the point you have plotted move down 2 units and to the right one unit.
3) Do this until you intersect with the y-axis (at -13), this is your value for 'b'
4) Plug your values for 'b' and 'm' into the slope-intercept equation